That's how hardware-accelerated video decoding used to work in Windows XP days IIRC (before GPU-based desktop composition), the video player would be a blank bl

That's how hardware-accelerated video decoding used to work in Windows XP days IIRC (before GPU-based desktop composition), the video player would be a blank black square and the GPU would be told to draw the video on those coordinates. Because of how it was implemented, you could drag VLC around while the video was playing and the video would stay "behind" everything, with the VLC window acting as a "hole" through which you could see it. (So you could move the window to the left and see half a black square on the left, and the left-most half of the video on the right) Nowadays with desktop composition AKA DWM, Windows just makes sure to black out DRM content from any frames/video it sends to an app requesting to capture the screen, making sure to send the video-including composed desktop only to the display. (And if you have some GPU recording software like NVIDIA ShadowPlay, it switches off when DRM content starts playing) You can see it in action with the Netflix UWP app. Of course, a bunch of DRM-respecting software -- like Netflix in Google Chrome -- doesn't really follow that spec and can still be screenshot/video captured like any app.